mixing oil weights?

Hey, a fellow rider mixed his oil weights in his soft tail, I was wonder if anyone ? GLIDER could tell me what this can cause in the long run? I was wondering what the oils did when mixed? one was 10/40 the other 20/50 do the oils seperate due to the weights?

It's not a bad thing to do but with different additives in the different oils there may be something that doesn't play together very well. I would stick with the same brand/ weight if there is a choice.